Adjacent channel interference (ACI) is one of the major impairments that can reduce achievable capacity in a satellite, especially in a high capacity throughput satellite (HTS) with densely packed spot beams. Adjacent channel interference arises due to leakages in channel filters used in satellite repeaters. Because most filters are finite response filters, adjacent channel interference can always be present. The most common technique to suppress ACI is to design multi-pole Butterworth filters with exceedingly steep roll-offs and thus quite low leakages. However, the steeper the filter is, the higher its insertion loss, and the more costly the filter can get.
The current ground system for communication satellites assigns carriers to users randomly from a total bandwidth pool, independent of a location of the requesting users. In order to mitigate ACI impairment, satellite operators often impose very stringent ACI specifications to the spacecraft manufacturers, for example, about 30 dB or higher over the temperature range and life of the satellite. Spacecraft manufacturers have to deal with fabricating and implementing very difficult filters in order to meet the ACI specification, which can naturally drive up the cost and delay the schedule.